A communications network can be generally defined as a collection of network nodes and end nodes interconnected through communications links or transmission groups. A network node can be characterized as a data processing system that provides certain functions within the network, such as routing of messages between itself and its adjacent or neighboring nodes, selection of routes for messages to be transmitted between a network node and an end node and the furnishing of directory services to connected end nodes. The links between nodes may be permanent communications links such as conventional cable connections or links that are enabled only when needed, such as dial-up telephone connections. End nodes are exemplified by devices such as display terminals, intelligent workstations, printers and the like which do not provide routing or route selection or directory services to other nodes in the network. Collectively, the network nodes, the end nodes and the transmission groups between the nodes are referred to as network resources. The physical configuration and characteristics of the various nodes and links (and their state) in a network are said to be the topology of the network.
Before a message can be transmitted between any two nodes in any network, a human operator or data processing equipment responsible for establishing the connections needs an accurate and up-to-date file or database on the network topology.
Successful attempts have been made to have the network equipment itself take over the task of maintaining a topology database without human intervention. For example, each processor performing a communication control function can notify other processors of changes in the status of its resources. The other processors use these topology update messages to amend or change their own copies of the topology network database.
In a distributed computing system, several networks may connect the nodes that comprise the system. It is possible that not all nodes are connected to all networks, and multiple “hops” may be needed to transmit messages between any two nodes that are not connected to the same network. To accomplish this, all nodes within the system must know the current global network topology. The topology information includes the set of nodes and network adapters that are connected to each of the networks in the system, as well as the set of adapters and networks that are down. The topology information changes each time a node, network, or network adapter fails or is powered up. Using the global network topology, each node is able to compute the set of reachable nodes and the route to each reachable node.
A need exists in the art for an enhanced technique for disseminating the global topology information to all nodes in the system. More particularly, there is a need for an enhanced topology propagation technique which ensures that there is no propagation of topology messages within the distributed computing environment when the system is in steady state, that is, when no nodes or network adapters fail or are powered up. Preferably, this enhanced technique is achieved without the use of explicit message acknowledgments. The present invention is directed to providing such a topology propagation mechanism.